This application relates to a refrigerant system having a reheat function provided by hot refrigerant in a bypass line.
Refrigerant systems are utilized in applications to change the temperature and humidity or otherwise condition the environment. In a standard refrigerant system, a compressor delivers a compressed refrigerant to a heat exchanger, known as a condenser, which is typically located outside. From the condenser, the refrigerant passes through an expansion device, and then to an indoor heat exchanger, known as an evaporator. At the evaporator, moisture may be removed from the air, and the temperature of air blown over the evaporator coil is lowered. From the evaporator, the refrigerant returns to the compressor. Of course, basic refrigerant cycles are utilized in combination with many configuration variations and optional features. However, the above provides a brief understanding of the fundamental concept.
In some cases, while the system is operating in a cooling mode, the temperature level at which the air is delivered to provide a comfort environment in a conditioned space may need to be higher than the temperature that would provide the ideal humidity level. Generally, the lower the temperature of the evaporator coil is the more moisture can be removed from the air stream. These opposite trends have presented challenges to refrigerant system designers. One way to address such challenges is to utilize various schematics incorporating reheat coils. In many cases, a reheat coil placed in the way of an indoor air stream behind the evaporator is employed for the purpose of reheating the air supplied to the conditioned space after it has been cooled in the evaporator, and where the moisture has been removed from the air as well.
Known reheat systems require additional components such as flow control devices, and are susceptible to refrigerant charge migration problems that may affect system operational characteristics, functionality and reliability over a wide range of environmental and operating conditions. Of course, it is typically beneficial to reduce refrigerant system schematic and control complexity as well as to avoid potential reliability issues.
Also, an unloader or bypass function is often provided in a refrigerant system. In such a function, a portion of the refrigerant is bypassed from an intermediate compression point at the compressor back to the suction line of the compressor. This bypass or unloaded operation is utilized when the system demand for cooling capacity is lower than it might otherwise be. In such a case, by diverting a portion of the refrigerant back to the compressor suction and bypassing other system components, the load on the compressor and other components is reduced. At the same time, the temperature of the combined refrigerant flow (form the bypass and from the evaporator) at the compressor suction is increased, potentially negatively impacting compressor reliability and reducing the mass flow rate the compressor is capable of pumping through.
In some cases, when there is no an intermediate port incorporated in the compressor design, a so-called hot gas bypass is utilized for the unloading function. In such systems, hot discharge refrigerant vapor is diverted back to the compressor suction port (or sometimes to the evaporator inlet), having been passed through an expansion device first to reduce its pressure. As before, the temperature of the combined refrigerant flow at the compressor suction is increased, which may be detrimental for compressor reliability and may negatively impact compressor performance.